An audio compressing technology is a core of multimedia application technologies such as digital audio broadcasting, and music dissemination and audio communication on the Internet. Transform coding is a commonly used method in the audio compressing technology. During transform coding, audio data is transformed from a data domain to another data domain, so that a large amount of information in the audio data can be represented by using less data, which helps quantize the audio data to achieve an objective of efficient compression coding.
According to an existing transform coding algorithm, an encoder transforms an audio signal from a time domain to a frequency domain (time-frequency transformation) to obtain spectral coefficients of the audio signal, splits the spectral coefficients into subbands, calculates and quantizes frequency envelopes of the subbands to obtain index values of quantized frequency envelopes of the subbands and values of the quantized frequency envelopes of the subbands, then, separately performs bit allocation for spectral coefficients of the subbands according to the values of the quantized frequency envelopes of the subbands and a quantity of available bits, quantizes the spectral coefficients of the subbands according to the values of the quantized frequency envelopes of the subbands and quantities of bits allocated to the spectral coefficients of the subbands, and finally, writes the index values of the quantized frequency envelopes of the subbands and the quantized spectral coefficients of the subbands into a bitstream and transmits the bitstream to a decoder.
However, when bit allocation is performed for the spectral coefficients of the subbands in the prior art, quantization bit allocation is performed for the spectral coefficients of the subbands according to the values of the quantized frequency envelopes of the subbands, which may cause improper quantization bit allocation for spectral coefficients of some subbands, and cause low quality of a signal obtained by the decoder by means of decoding.